Sprocket for bicycle

ABSTRACT

In a sprocket for a bicycle having a radial bearing acting as a bearing portion, an axial load acting on the bearing can be easily adjusted without having to dismount the components of the bicycle after the bicycle has been assembled. 
     An elastomer is used as a component for an anti-rotation mechanism of an adjusting nut which serves to adjust the axial load of the radial bearing, so that an excessive load is not applied on the radial bearing, which would result in a defective rotation. Further, the axial load acting on the radial bearing can be easily adjusted without having to dismount the components of the bicycle after the bicycle has been assembled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sprocket for a bicycle.

2. Description of the Related Art

Recently, a sprocket having a radial bearing is widely used for thereason that adopting the radial bearing can enhance the precision of thebearing portion and make it superior in durability.

However, once the relative position between the inner race and the outerrace of the radial bearing in an axial direction has a deviation, itwill cause a defective rotation. As a certain amount of load may effecta deviation in the relative position between the inner race and theouter race in an axial direction, and result in a defective rotation, aload like that should be avoided. However, it is necessary to preload acertain amount of load with which swing is not felt in the least, eventhough a rider pedals a bicycle.

In a prior example as shown in FIG. 3, a left crank is mounted on ashaft with two fixing bolts disposed in the direction perpendicular tothe shaft loosely. First, temporarily fixing bolts disposed in the axialdirection of the shaft are fastened not to cause the crank to make adefective rotation and an axial swing. Next, the two fixing boltsdisposed in the direction perpendicular to the shaft are fastened withequal forces, so that an axial force will not be generated with the leftcrank locked on the shaft. If the fastening forces of the two bolts arenot equal, the two bolts and the left crank may be gradually looseningin use. Therefore, a beginner is required to perform a hard operation,due to the fact that it can be not adjusted after the left crank hasbeen mounted.

In another prior example as shown in FIG. 4, fixing bolts disposed in adirection perpendicular to a shaft are fastened, such that a left crankcan not be loosened any more even though a rider pedals a bicyclecontinuously for a long time. The left crank is secured through afriction to a shaft, or is secured at a locking position to a lockingportion provided. At this time, an axial force is not applied to abearing by the left crank, directly, but indirectly through an elastomertherebetween. As the force is blocked by the elastomer, it can be setwithout rendering a defective rotation and an axial swing. However, withthe elastomer therebetween, when a large force is applied from the leftcrank side toward a right crank, the shaft will move temporarily towardthe right crank to cause an adverse effect on a driving system. Hence,it can be not adjusted after the left crank has been mounted.

In a still further prior example as shown in FIG. 5, a shaft insertedinto a left crank and secured therein passes through a sleeve 3, a leftbearing and a right bearing, and then extends into a right crank. Anadjusting nut is fastened to a screw thread portion matching with theadjusting nut without causing the shaft to swing. The screw threadportion for the adjusting nut is disposed at a base portion of the shaftfor securing the right crank. Next, the portion for securing the rightcrank which is outside the adjusting nut, is inserted into the rightcrank, and then, fixing bolts, which are disposed in the directionperpendicular to the shaft are fastened, such that the right crank willnot be loosened any more even though a rider pedals a bicyclecontinuously for a long time. At this time, the right crank abuts theend face of the adjusting nut. An axial force is applied to theadjusting nut by the right crank. Since a sleeve 1 and a sleeve 2 aredisposed between the outer races and the inner races of the right andleft radial bearings and the relative position of the outer races andthe inner races forming the bearings remains unchanged, the forceapplied to the bearings will not cause the bearings to render adefective rotation. Because the right crank abuts the end face of theadjusting nut, the adjusting nut can not be loosened to change theadjustment. However, this method can not make an adjustment aftermounting, either.

SUMMARY OF THE INVENTION

A sprocket for a bicycle is provided in which a radial bearing is usedto act as a bearing portion and in which an axial load on the bearingcan be easily adjusted without dismounting the components of thebicycle, even after the bicycle has been assembled.

After a shaft is mounted in a radial bearing, an adjusting nut foradjusting axial load is disposed on the shaft. Next, an anti-rotationmechanism provided with an elastomer is disposed, such that theadjusting nut will not be loosened or tightened up automatically whenrunning a bicycle. Furthermore, when a left crank is combined with theelasmoter, no excessive load is to be applied to the radial bearing.With the anti-rotation mechanism having the elastomer, even though thesprocket is mounted, an axial load on the radial bearing can be easilyadjusted without dismounting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred embodiment for the present invention.

FIG. 2 is an exploded perspective view of the left part of theembodiment of FIG. 1.

FIG. 3 shows a first embodiment of the prior art.

FIG. 4 shows a second embodiment of the prior art.

FIG. 5 shows a third embodiment of the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A shaft, which has already been put into a right crank and securedtherein, is inserted from a radial bearing at the right side of abicycle and protrudes from another radial bearing at the left side ofthe bicycle. Further, an adjusting nut is fastened to a thread portionof a screw in a way of not causing a defective rotation and an axialswing. The thread portion of screw is disposed at a base portion of aregion for determining the angle of a left crank and press-fitting theleft crank. As described later, the rotation of the adjusting nut isrestrained by a lock washer, provided with a pawl portion opposite tothe adjusting nut.

Next, the lock washer having a hole slightly larger than a profile of aportion of the shaft for restraining rotation with respect to the leftcrank and press-fitting the shaft and is secured around the shaft withthe pawl portion facing the right crank side.

The lock washer is restrained from rotating based on the shape of theshaft. When the adjusting nut and the pawl portion of the lock washerface to and are engaged with each other, the adjusting nut is restrainedfrom rotating indirectly due to a friction induced from the pawlportion. Here, the friction can be obtained from the pawl portion, butthe way to obtain the friction is not limited to the pawl portion.

Subsequently, an elastomer is mounted on the shaft. In FIG. 2, a wavespring washer is shown, but it is not limited to this. The adjustingnut, the lock washer, and the elastomer are arranged in this order(referring to FIG. 2).

Next, the left crank is mounted on the shaft and is secured by a fixingbolt. As such, the left crank makes the elastomer compressed anddeformed to generate an axial force. With this axial force, the lockwasher is pushed toward the adjusting nut to enhance a lock effect ofthe lock washer. For the embodiment using the radial bearing, the reasonwhy the adjusting nut is sometimes loosened and sometimes tightened upis due to vibration or twist. Basically, a turning force can not begenerated to render the adjusting nut sometimes loosened and sometimestightened up. Therefore, a force for making the elastomer compressed anddeformed is previously set in order not to cause the radial bearing adefective rotation.

When riding the bicycle, the right crank, the shaft, a right dust cover,the inner race of the right bearing, the inner race of the left bearing,a left dust cover, the lock washer, the adjusting nut, the elastomer,the left crank, etc are rotated together, that is to say not only theadjusting nut is naturally rotated. However, the adjusting nut ispressed by the elastomer with the lock washer located therebetween.Therefore, in the case of securing the crank, only the adjusting nut isloosened or tightened up, with an effect that an axial load on thebearing can be adjusted without disassembling of the sprocket, and, withthe pawl portion, a fine axial load can be easily adjusted.

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. FIG. 1 shows an embodiment of thepresent invention. FIG. 2 is an exploded perspective view of the leftpart of the embodiment as shown in FIG. 1 of the present invention.FIGS. 3 and 4 show 3 kinds of prior arts respectively.

According to the present invention, as shown in FIG. 1 on a shaft, thereare disposed key slots 5 a for restraining rotation with respect to aright crank and for press-fitting fixation; a thread portion 5 b ofscrew, on which an adjusting nut 18 having a pawl portion can bescrewed; a portion 5 c for restraining the rotation with respect to aleft crank 2 and for press-fit mounting; and a thread portion 5 d ofscrew, on which a fixing bolt 15 can be screwed to secure the leftcrank.

Key slots 1 a for restraining the rotation of the right crank 1 withrespect to the shaft 5 and for press-fitting fixation are disposed onthe right crank 1. The key slots 5 a of the shaft 5 are engaged with thekey slots la to make the right crank 1 and the shaft 5 integratedtogether. Then, large gears 3 and small gears 4 are fixed by using bolts10, bolts 12 and nuts 11. A gear ratio can be selected so that a chaincan be derailed onto a selected gear.

A deformation hole 2 a and a thread portion 2 b of screw for restrainingrotation of the left crank 2 with respective to the shaft 5 and forpress-fitting fixation are disposed on the left crank 2. A cap bolt 16can be fastened on the thread portion 2 b of screw. The cap bolt 16 canbe designed to make the sprocket assembled/disassembled by merely usinga hex wrench. After a washer 17 and the fixing bolt 15 put inside thethread portion 2 b of screw, the cap bolt 16 is fastened. When thefixing bolt 15 is loosened to dismount the left crank 2, the head 15 aof the fixing bolt touches the inner side 16 a of the cap bolt, andhence the left crank 2 comes out gradually. On the left crank 2, thereis a side face 2 c abutting an elastomer 20.

On the right side of a bottom bracket shell 14, there are mounted aright bowl 6 and a spacer 13 in which a bearing 8 and a dust cover 9 arefitted inside the bowl 6, and the spacer 13 is corresponding to aportion of the bottom bracket shell 14 having a different width.Additionally, the dust cover 9 only abuts the inner race 8 a of thebearing 8.

On the left side of the bottom bracket shell 14, there are mounted aleft bowl 7 and a spacer 13, in which a bearing 8 and a dust cover 9 arefitted inside the bowl 7, and the spacer 13 is corresponding to aportion of the bottom bracket shell 14 having a different width.Additionally, the dust cover 9 only abuts the inner race 8 a of thebearing 8.

The shaft 5 is first put into the right crank 1 and secured therein, andthen is inserted into the above-assembled bottom bracket. The adjustingnut 18 having a pawing portion facing the left crank side is fastenedonto the thread portion 5 b of screw at the front end of the shaft 5without causing a defective rotation and an axial swing, thereby theright crank is mounted on the bottom bracket.

The lock washer 19, which is outside the adjusting nut 18 and therotation of which is restrained by the shaft 5, is secured around theshaft 5 with a pawl portion facing the right crank, the pawl portion ofthe adjusting nut and the pawing portion of the lock washer beingengaged with each other.

The elastomer 20 is secured outside the lock washer 19.

By means of the fixing bolt 15 being screwed with a screw thread 5 d atthe central portion of the shaft 5, the left crank 2 is mounted outsidethe elastomer 20 with the rotation of the left crank 2 restrained by theportion 5 c of the shaft 5.

The side face 2C of the left crank 2 which is opposite to the rightcrank side is formed to compress the elastomer 20 in the axialdirection. Then, the induced compression force is press the lock washer19 toward the adjusting nut 18. A friction resistance generated by theengagement of the adjusting nut 18 with the opposite pawl is used inorder not to make the adjusting nut sometimes loosened and sometimestightened up. With the elastomer provided between the left crank 2 andthe bearing 8, an excessive load will not be applied to the bearing, andhence a defective rotation is avoided.

As shown in the drawings, the lock washer is located between theadjusting nut 18 and the elastomer with the adjusting nut 18 beingpressed by the elastomer indirectly. Hence, if the crank is secured, theadjusting nut 18 can be turned to adjust the axial load on the bearing.

Although, the shaft is secured in the right crank, as shown in thepresent embodiment, yet the shaft can be secured in the left crank, too.The sprocket has two gears as shown in the present invention, but asprocket having one gear or three gears is applicable, too.

With regard to a prior sprocket provided with a radial bearing, foravoiding an excessive load from occurring in an axial direction to causea defective rotation, a left crank having a cut-out is secured byfastening a bolt in a direction perpendicular to the shaft. However, thecut-out will degrade the strength of the left crank. Therefore, it isnecessary to reinforce the wall thickness of the left crank, whichresulting in the weight of the left crank becoming too heavy such thatthe axial load can not be adjusted after an assembly is made.

Also, in order to minimize the left crank, a bolt-insertion portion isprovided in the axial direction of the shaft of the left crank and abolt is fastened into the shaft for securing the left crank. Moreover,for preventing an excessive load generating in the axial direction frombeing applied on the radial bearing, an elastomer is providedtherebetween. However, when a large force is applied in the axialdirection, the elastomer is compressed to cause the shaft to be moved inthe axial direction, which renders an adverse effect on a drivingsystem. After continuous use for a long time, the elastomer may bedeformed, and causing an axial swing.

The present invention is to resolve the above problems of the priorarts. In order to minimize a left crank, a bolt insertion portion isprovided in the axial direction of a shaft in the left crank and a boltis fastened into the shaft for securing the left crank. As an elastomeris provided therebetween, an excessive load will not be applied on theradial bearing. Even though a large force is applied in the axialdirection, this force is received by the adjusting nut, instead of bythe elastomer. Due to the fact that the shaft can not be moved in theaxial direction, no adverse effect will be caused on a driving system.For the prior arts, after an assembly is made, an adjustment can not bemade. Even though it was not a best adjustment, you can only accept it.However, according to the present invention, after assembly, anadjustment can be made. Therefore, the present invention is very muchhelpful for users.

What is claimed is:
 1. A sprocket for a bicycle, comprising: a radialbearing acting as a bearing portion; a shaft adapted to be inserted intoa right crank and secured therein; a left crank having a side, at whichmounting and dismounting of the left crank are performed; an adjustingnut, for applying an appropriate axial force on the bearing; a lockwasher, for preventing the adjusting nut from loosening; and anelastomer, for preventing an excessive force from being applied on theradial bearing during the mounting of the left crank, which would resultin a defective rotation, and for enhancing a locking function of thelock washer.